The present invention relates to an acetabular cup for receiving the ball of a femoral hip joint prosthesis.
Acetabular cups and acetabular cup assemblies of various types have long been used in hip joint replacement surgery. In such surgery, a femoral hip joint prosthesis formed of a suitable metal such as a cobalt chrome molybdenum alloy or other FDA approved material is implanted in the femur. The femoral hip joint prosthesis has an associated spherical-shaped ball. It is necessary to implant an acetabular cup or acetabular cup assembly in the acetabulum in a cavity which has been prepared by the surgeon for the purpose of receiving the spherical-shaped ball.
The artificial socket (i.e., acetabular cup or acetabular cup assembly) in which the ball of the femoral hip joint prosthesis is to be positioned is formed of a material other than metal and is frequently formed of a suitable biocompatible plastic such as a high molecular weight polyethylene (HMWPE) as this provides a natural lubricity which permits the ball to freely rotate in the cup socket.
In some instances, the acetabular cup is a single unitary device which is implanted in a prepared cavity of the acetabulum using a suitable bone cement such as polymethlymethacrylate (PMMA). In other instances, depending upon the condition of the patient and/or the preference of the surgeon, an acetabular cup assembly consisting of multiple units including a metal shell and a plastic cup-shaped insert may be used. In the latter instance, the metal shall may be affixed in the prepared cavity of the acetabulum by a variety of means including screws joining the metal shell directly to the acetabulum or a friction fit in the cavity with a shell having an exterior surface of a type which is roughened, coated or formed with interstices which will promote bone ingrowth therein. Examples of one-piece acetabular cups are shown in U.S. Pat. Nos. 3,829,904; 3,986,212 and the FIG. 1 embodiment of U.S. Pat. No. 5,009,665. Examples of multiple-piece acetabular cup assemblies are shown in the FIGS. 2-4 embodiments of U.S. Pat. No. 5,009,665 and in U.S. Pat. Nos. 4,704,127; 4,695,282; 5,002,577 and 5,019,105. The foregoing prior art patents are hereby incorporated by reference in this application.
Heretofore, plastic cup members intended for use as a single unitary unit were manufactured to one of various designs depending upon the manufacturer and plastic cup members intended for use with a separate shell member to form an acetabular cup assembly were designed and manufactured to different configurations even in those instances where a single manufacturer produced both the unitary type and the multiple component assembly type of acetabular cup prosthesis. This, of course, required that the manufacturer have one mold for forming a plastic member intended for the unitary acetabular cup prosthesis and a different mold for forming the plastic cup member of the same size intended for use with a metal shell for an acetabular cup assembly. As is well known, the plastic acetabular cups come in a wide variety of sizes and a separate mold is required for each size cup. Heretofore, the fact that different designs of plastic acetabular cups were used for unitary acetabular cup prostheses than for acetabular cup assemblies required that the hospital carry separate inventories of plastic cups, one set for the unitary version and a second set for the multiple component version, with several sizes required for each such set.